internal bool Checksum(string value, string checksum)
{
value = ConvertToNumeric(value);
char[] charArr = value.Where(char.IsLetterOrDigit).ToArray();
List <int> digitsToCheck = charArr.Select(character =>
char.IsLetter(character)
? _checksum.GetIndexInAlphabet(character)
: (int)char.GetNumericValue(character))
.ToList();
return(_checksum.PerformChecksum(digitsToCheck, int.Parse(checksum)));
}